Grind the mustard seeds in a mortar and pestle or a spice mill. Place the ground mustard seeds in a bowl with enough water to moisten and allow them to sit for 10 minutes. Replace the soaked seeds in the mortar or the bowl of a food processor and process with the remaining ingredients until the desired consistency is reached. Spoon the mustard into a small jar and cover tightly. The mustard should sit for at least 2 weeks before use.